Improving network lifetime is a fundamental challenge of wireless sensor networks. One possible solution consists in making use of mobile sinks. Whereas theoretical analysis shows that this approach does indeed benefit network lifetime, practical routing protocols that support sink mobility are still missing. In this paper, in line with our previous efforts, we investigate the approach that makes use of a mobile sink for balancing the traffic load and in turn improving network lifetime. We engineer a routing protocol, MobiRoute, that effectively supports sink mobility. Through intensive simulations in TOSSIM with a mobile sink and an implementation of MobiRoute, we prove the feasibility of the mobile sink approach by demonstrating the improved network lifetime in several deployment scenarios.I. INTRODUCTION Many proposals on using mobile sinks to improve the lifetime of wireless sensor networks (WSNs) have appeared recently [1,2,3,4,5,6,7,8,9]. However, in the research community there is a doubt that moving sinks is practical (e.g., [10]). One of the major concerns behind this doubt is that mobility inevitably incurs additional overhead in data communication protocols and the overhead can potentially offset the benefit brought by mobility. In this paper, we intend to dismiss the doubt.We focus on a scenario where all nodes are fixed and have limited energy reserves and where a mobile sink endowed with significantly more resources serves as the data collector. In this scenario, the sink mobility can increase network lifetime through two different methods, depending on the relationship between the sink moving speed and the tolerable delay of the data delivery.In the fast mobility regime, the speed produces tolerable data delivery delay. The WSNs may then take advantage of mobility capacity [11]. This mobile relay approach [1, 2, 3] uses the mobile sink to transport data with its mechanical movements. It trades data delivery latency for the reduction of node energy consumption. We refer to [3] and [4] for simulations and field studies in this regime. In the slow mobility regime, the sink mobility takes a discrete form: the movement trace consists of several anchor points between which the sink moves and at which it pauses. Consequently, the network cannot benefit from mobility capacity. However, it has recently been observed [5,6,7,8,9] that sink mobility can still improve network lifetime. The reason is that the typical many-to-one traffic pattern in WSNs imposes a heavy forwarding load on the nodes close to sinks. While no energy conserving protocol alleviates such a load, moving the sink (even very infrequently) can distribute over time the role of bottleneck nodes and thus even out the load. Unfortunately, theoretical analysis [5,6,7,8,9] may produce misleading results due to its simplified system model (an example is given in Section V: footnote 4); simulations involving a detailed protocol implementation are necessary to fully understand the benefit of using mobile sinks.We argue that the slow mobili...

COMMONSense Net (CSN) is an ongoing research project that focuses on the design and implementation of a sensor network for agricultural management in developing countries, with a special emphasis on the resource-poor farmers of semiarid regions. Throughout the year 2004, we carried out a survey on the information needs of the population living in a cluster of villages in Southern Karnataka, India. The results highlighted the potential that environment-related information has for the improvement of farming strategies in the face of highly variable conditions, in particular for risk management strategies (choice of crop varieties, sowing and harvest periods, prevention of pests and diseases, ef�cient use of irrigation water, etc.). Accordingly, we advocate an original use of information and communication technologies (ICT). Our demand-driven approach for the design of appropriate ICT tools that are targeted at the resource-poor, we believe, is relatively new. In order to go beyond a pure technocratic approach, we adopted an iterative, participatory methodology. (c) 2007 by The Massachusetts Institute of Technology.

Wireless sensor networks (WSNs) can be a valuable decision-support tool for farmers. This motivated our deployment of a WSN system to support rain-fed agriculture in India. We defined promising use cases and resolved technical challenges throughout a two-year deployment of our COMMON-Sense Net system, which provided farmers with environment data. However, the direct use of this technology in the field did not foster the expected participation of the population. This made it difficult to develop the intended decision-support system. Based on this experience, we take the following position in this paper: currently, the deployment of WSN technology in developing regions is more likely to be effective if it targets scientists and technical personnel as users, rather than the farmers themselves. We base this claim on the lessons learned from the COMMON-Sense system deployment and the results of an extensive user experiment with agriculture scientists, which we describe in this paper.

Abstract-We describe the on-going design and implementation of a sensor network for agricultural management targeted at resource-poor farmers in India. Our focus on semi-arid regions led us to concentrate on water-related issues. Throughout 2004, we carried out a survey on the information needs of the population living in a cluster of villages in our study area. The results highlighted the potential that environment-related information has for the improvement of farming strategies in the face of highly variable conditions, in particular for risk management strategies (choice of crop varieties, sowing and harvest periods, prevention of pests and diseases, efficient use of irrigation water etc.). This leads us to advocate an original use of Information and Communication Technologies (ICT). We believe our demand-driven approach for the design of appropriate ICT tools that are targeted at the resource-poor to be relatively new. In order to go beyond a pure technocratic approach, we adopted an iterative, participatory methodology.

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